The present invention relates in general to pulse oximetry, and in particular to the processing of signals generated by a pulse oximeter.
A pulse oximeter is typically used to measure various blood characteristics including the blood oxygen saturation of hemoglobin in arterial blood and the pulse rate of the patient. Measurement of these characteristics has been accomplished by use of a non-invasive sensor that passes light through a portion of a patient's blood perfused tissue and photo-electrically senses the absorption and scattering of light in such tissue. The amount of light absorbed and scattered is then used to estimate the amount of blood constituent in the tissue using various algorithms known in the art. The “pulse” in pulse oximetry comes from the time varying amount of arterial blood in the tissue during a cardiac cycle. The signal processed from the sensed optical measurement is the familiar plethysmographic waveform, which corresponds with the cyclic attenuation of optical energy through a portion of a patient's blood perfused tissue.
Various physiological and/or external factors can adversely impact the accuracy and/or the reliability of physiological parameters that are estimated by a pulse oximeter. These undesirable factors are sometimes referred to as artifacts. Artifacts in general and correlated artifacts in particular can be caused by motion, respiratory artifact, or electronic interference. Correlated artifact is an artifact that perturbs more than one of the signals that are provided by an oximeter sensor, and where the perturbations are largely correlated between those signals.
It is desirable for a pulse oximetry system to be able to perform its calculations in the presence of correlated artifacts.